There is known a keyless entry system or an engine starter system. The keyless entry system performs wireless communication between a mobile device carried by a user in a vehicle and an onboard device mounted on the vehicle. The keyless entry system locks or unlocks a vehicle door when the onboard device receives a unique authentication code from the mobile device. In this case, the engine starter system starts a vehicle machine such as an engine.
This type of vehicle control system includes a mobile-based transmission type and a vehicle-based transmission type. According to the mobile-based transmission type of vehicle control system, for example, the mobile device transmits a wireless signal (mobile signal) when detecting user's manipulation as a trigger such as pressing on the mobile device. The onboard device transmits a wireless signal (vehicle signal) when detecting reception of the mobile signal as a trigger. According to the vehicle-based transmission type of vehicle control system, for example, the onboard device transmits a vehicle signal when detecting user's manipulation as a trigger such as touching a door handle or pressing a starter button in a vehicle compartment. The mobile device transmits a wireless signal (mobile signal) when detecting reception of the vehicle signal as a trigger.
In this vehicle control system, for example, the onboard device determines whether or not the mobile device is located within an effective area around a specified place (vehicular place) in a vehicle. When determining that the mobile device is located within the effective area, the onboard device receives the authentication code and provides vehicle control over a door or an engine.
The effective area is predetermined for each of manufacturers. Too wide an effective area allows the onboard device to communicate with the mobile device distant from the vehicle and increases a risk of permitting a third party near the vehicle to enter or drive the vehicle. Too narrow an effective area necessitates a user to closely approach the vehicle for remote control and increases a risk of degrading usability. For this reason, respective manufactures strictly predetermine the effective area as a distance (between the mobile device and the vehicular place) that avoids these risks.
However, the vehicle control system is reconsidered to replace a dedicated mobile device with a mobile communication terminal such as a mobile telephone or a smart phone. This improves usability because a user need not own a dedicated mobile device in addition to a mobile communication terminal the user already owns.
For example, the mobile communication terminal transmits a mobile signal to the onboard device. A mobile signal transmission output depends on models of mobile communication terminals. The onboard device strictly determines whether or not the mobile communication terminal is located within the effective area, based on the mobile signal reception strength. For this purpose, the onboard device is proposed to previously store correction information that corrects the mobile signal reception strength (e.g., see patent literature 1).